1. Field of the Invention
The present invention relates to a medium exhibiting negative refraction, and an optical system which includes an optical element formed of such a medium.
2. Description of the Related Art
Conventionally, there has been well known: an optical element using an optical or electromagnetic wave; an optical system such as an image pickup optical system, an observation optical system, a projection optical system and a signal processing system; and an optical device using them. These optical systems have had a disadvantage that image resolution is limited due to diffraction caused by undulation property of an optical or electromagnetic wave.
In order to overcome this disadvantage, the following non-patent documents 2 and 5, etc. describe that a negative refractive index medium is used as a technique for achieving image formation which exceeds the diffraction limit.
FIG. 16 is an illustrative view showing image formation using a parallel flat plate 380 formed of a negative refractive index medium 301. In FIG. 16, t0 denotes a distance between an object point and a left side face of the flat plate 380; t0′ denotes a distance between an image point and a right side face of the flat plate 380; “t” denotes a thickness of the flat plate 380; “i” denotes an incident angle; “r” denotes a refractive angle; and ns denotes a refractive index of the negative refractive index medium 301 to a vacuum.
A refractive index at the periphery of the flat plate 380 is defined as n0, and n0=1 is established in the case of a vacuum. FIG. 16 shows a case in which n0=1 and ns=−1 are established.
The arrow indicates an emitted light component among the light beams emitted from an object. Because a refraction law is established according to non-patent document 2, the following formula is established:n0 sin i=ns sin r  Formula (101)Assuming that n0=1 and ns=−1, the following formula is established:r=−i  Formula (102)Therefore, a light beam of the emitted light component is formed as an image point at a point at which t0′ satisfies the following formula:t0+t0′=t  Formula (103)
On the other hand, an evanescent wave generated from an object point is produced as intensity equal to that of the object point at a point at which t0′ satisfies formula (103). All the light beams emitted from the object are collected at the image point, and thus, image formation exceeding the diffraction limit is achieved. This is referred to as complete image formation. It is known from non-patent document 2 listed below that, even if the periphery of the negative refractive index medium 301 is not a vacuum, complete image formation is achieved when formula (103) and the following formula are satisfied:ns=−n0  Formula (104)Non-Patent Document 1:
Mechanism and application of optical system, 73-77, 166-170, Optronics Co., Ltd., 2003
Non-Patent Document 2:
J. B. Pendtry Phys. Rev. Lett., Vol 85, 18 (2000) 3966-3969
Non-Patent Document 3:
M. Notomi Phys. Rev. B. Vol 62 (2000) 10696
Non-Patent Document 4:
V. G. Veselago Sov. Phys. Usp. Vol. 10, 509-514 (1968)
Non-Patent Document 5:
L. Liu and S. He Optics Express Vol. 12 No. 20 4835-4040 (2004)
Non-Patent Document 6:
Sato & Kawakami, Optronics, 2001, July issue, page 197
Patent Document 1:
US 2003/0227415 A1
Patent Document 2:
US 2002/0175693 A1